Nanosheet FET bottom isolation

ABSTRACT

A technique relates to a semiconductor device. A rare earth material is formed on a substrate. An isolation layer is formed at an interface of the rare earth material and the substrate. Channel layers are formed over the isolation layer. Source or drain (S/D) regions are formed on the isolation layer.

BACKGROUND

The present invention generally relates to fabrication methods andresulting structures for semiconductor devices, and more specifically,to nanosheet FET bottom isolation.

In contemporary semiconductor device fabrication processes, a largenumber of semiconductor devices, such as n-type field effect transistors(nFETs) and p-type field effect transistors (pFETs), are fabricated on asingle wafer. Non-planar transistor device architectures, such asnanosheet (or nanowire) transistors, can provide increased devicedensity and increased performance over planar transistors. Nanosheettransistors, in contrast to conventional planar FETs, include a gatestack that wraps around the full perimeter of multiple nanosheet channelregions for improved control of channel current flow. Nanosheettransistor configurations enable fuller depletion in the nanosheetchannel regions and reduce short-channel effects.

SUMMARY

Embodiments of the invention are directed to a method for forming asemiconductor device. A non-limiting example of the method includesforming a rare earth material on a substrate, forming an isolation layerat an interface of the rare earth material and the substrate, formingchannel layers over the isolation layer, and forming source or drain(S/D) regions on the isolation layer.

Embodiments of the invention are directed to a semiconductor device. Anon-limiting example of the semiconductor device includes a rare earthmaterial formed on a substrate, an isolation layer formed at aninterface of the rare earth material and the substrate, channel layersformed over the isolation layer, and source or drain (S/D) regionsformed on the isolation layer.

Embodiments of the invention are directed to a method for forming anisolation layer for a semiconductor device. A non-limiting example ofthe method includes forming a rare earth oxide material on a substrateand diffusing oxygen through the rare earth oxide material such that anoxide is grown at an interface of the rare earth oxide material and thesubstrate, the oxide being the isolation layer. Also, the methodincludes forming channel layers over the isolation layer and formingsource or drain (S/D) regions on the isolation layer.

Additional technical features and benefits are realized through thetechniques of the present invention. Embodiments and aspects of theinvention are described in detail herein and are considered a part ofthe claimed subject matter. For a better understanding, refer to thedetailed description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The specifics of the exclusive rights described herein are particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe embodiments of the invention are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1A depicts a simple diagram of a top view of a semiconductor deviceaccording to embodiments of the invention;

FIG. 1B depicts a cross-sectional view of the semiconductor device takenalong line X in FIG. 1A after fabrication operations according toembodiments of the invention;

FIG. 2 depicts a cross-sectional view of the semiconductor device takenalong line X (shown in FIG. 1A) after fabrication operations accordingto embodiments of the invention;

FIG. 3 depicts a cross-sectional view of the semiconductor device takenalong line X (shown in FIG. 1A) after fabrication operations accordingto embodiments of the invention;

FIG. 4 depicts a cross-sectional view of the semiconductor device takenalong line X (shown in FIG. 1A) after fabrication operations accordingto embodiments of the invention;

FIG. 5 depicts a cross-sectional view of the semiconductor device takenalong line X (shown in FIG. 1A) after fabrication operations accordingto embodiments of the invention;

FIG. 6 depicts a cross-sectional view of the semiconductor device takenalong line X (shown in FIG. 1A) after fabrication operations accordingto embodiments of the invention;

FIG. 7 depicts a cross-sectional view of the semiconductor device takenalong line X (shown in FIG. 1A) after fabrication operations accordingto embodiments of the invention;

FIG. 8 depicts a cross-sectional view of the semiconductor device takenalong line X (shown in FIG. 1A) after fabrication operations accordingto embodiments of the invention;

FIG. 9 depicts a cross-sectional view of the semiconductor device takenalong line X (shown in FIG. 1A) after fabrication operations accordingto embodiments of the invention;

FIG. 10 depicts a cross-sectional view of the semiconductor device takenalong line X (shown in FIG. 1A) after fabrication operations accordingto embodiments of the invention;

FIG. 11 depicts a cross-sectional view of the semiconductor device takenalong line X (shown in FIG. 1A) after fabrication operations accordingto embodiments of the invention;

FIG. 12 depicts a cross-sectional view of the semiconductor device takenalong line X (shown in FIG. 1A) after fabrication operations accordingto embodiments of the invention; and

FIG. 13 depicts a cross-sectional view of the semiconductor device takenalong line X (shown in FIG. 1A) after fabrication operations accordingto embodiments of the invention.

The diagrams depicted herein are illustrative. There can be manyvariations to the diagram or the operations described therein withoutdeparting from the spirit of the invention. For instance, the actionscan be performed in a differing order or actions can be added, deletedor modified. Also, the term “coupled” and variations thereof describeshaving a communications path between two elements and does not imply adirect connection between the elements with no interveningelements/connections between them. All of these variations areconsidered a part of the specification.

In the accompanying figures and following detailed description of theembodiments of the invention, the various elements illustrated in thefigures are provided with two or three digit reference numbers. Withminor exceptions, the leftmost digit(s) of each reference numbercorrespond to the figure in which its element is first illustrated.

DETAILED DESCRIPTION

For the sake of brevity, conventional techniques related tosemiconductor device and integrated circuit (IC) fabrication may or maynot be described in detail herein. Moreover, the various tasks andprocess steps described herein can be incorporated into a morecomprehensive procedure or process having additional steps orfunctionality not described in detail herein. In particular, varioussteps in the manufacture of semiconductor devices andsemiconductor-based ICs are well known and so, in the interest ofbrevity, many conventional steps will only be mentioned briefly hereinor will be omitted entirely without providing the well-known processdetails.

Turning now to an overview of technologies that are more specificallyrelevant to aspects of the invention, a metal-oxide-semiconductorfield-effect transistor (MOSFET) is used for amplifying or switchingelectronic signals. The MOSFET has a source, a drain, and a metal oxidegate electrode. The metal gate portion of the metal oxide gate electrodeis electrically insulated from the main semiconductor n-channel orp-channel by the oxide portion of the metal oxide gate electrode. Theoxide portion of the gate electrode can be implemented as a thin layerof insulating material, for example, silicon dioxide or glass, whichmakes the input resistance of the MOSFET relatively high. The gatevoltage controls whether the current path from the source to the drainis an open circuit (“off”) or a resistive path (“on”). N-type fieldeffect transistors (NFET) and p-type field effect transistors (PFET) aretwo types of complementary MOSFETs. The NFET includes n-doped source anddrain junctions and uses electrons as the current carriers. The PFETincludes p-doped source and drain junctions and uses holes as thecurrent carriers. Complementary metal oxide semiconductor (CMOS) is atechnology that uses complementary and symmetrical pairs of p-type andn-type MOSFETs to implement logic functions.

The wafer footprint of an FET is related to the electrical conductivityof the channel material. If the channel material has a relatively highconductivity, the FET can be made with a correspondingly smaller waferfootprint. A known method of increasing channel conductivity anddecreasing FET size is to form the channel as a nanostructure. Forexample, a so-called gate-all-around (GAA) nanosheet FET is a knownarchitecture for providing a relatively small FET footprint by formingthe channel region as a series of nanosheets. In a known GAAconfiguration, a nanosheet-based FET includes a source region, a drainregion and stacked nanosheet channels between the source and drainregions. A gate surrounds the stacked nanosheet channels and regulateselectron flow through the nanosheet channels between the source anddrain regions. GAA nanosheet FETs are fabricated by forming alternatinglayers of channel nanosheets and sacrificial nanosheets. The sacrificialnanosheets are released from the channel nanosheets before the FETdevice is finalized. For n-type FETs, the channel nanosheets aretypically silicon (Si) and the sacrificial nanosheets are typicallysilicon germanium (SiGe). For p-type FETs, the channel nanosheets can beSiGe and the sacrificial nanosheets can be Si. In some implementations,the channel nanosheet of a p-type FET can be SiGe or Si, and thesacrificial nanosheets can be Si or SiGe. Forming the GAA nanosheetsfrom alternating layers of channel nanosheets formed from a first typeof semiconductor material (e.g., Si for n-type FETs, and SiGe for p-typeFETs) and sacrificial nanosheets formed from a second type ofsemiconductor material (e.g., SiGe for n-type FETs, and Si for p-typeFETs) provides superior channel electrostatics control, which isnecessary for continuously scaling gate lengths down to seven (7)nanometer CMOS technology and below. The use of multiple layered SiGe/Sisacrificial/channel nanosheets (or Si/SiGe sacrificial/channelnanosheets) to form the channel regions in GAA FET semiconductor devicesprovides desirable device characteristics, including the introduction ofstrain at the interface between SiGe and Si.

For nanosheet devices formed on a bulk substrate, the source and drainregions are epitaxially grown from the side of the silicon nanosheetsand an upper surface of the silicon substrate. This leads to parasiticsource and drain leakage harming nanosheet FET performance.Particularly, the combination of the epitaxy contacting the substrate inthe source/drain region and the high-k metal gate (HKMG) stack formeddirectly on the substrate in the sub-fin region form a bottom parasiticplanar transistor that can degrade the performance of thegate-all-around nanosheet-FET. Accordingly, a better integration schemeis needed.

Turning now to an overview of the aspects of the invention, one or moreembodiments of the invention provide semiconductor devices and methodsof forming the semiconductor devices. Embodiments of the inventionprovide integration methods to form full bottom dielectric isolation ofnanosheet FETs by the oxygen diffusion through a rare earthoxide/silicon substrate interface. For example, a rare earth oxidebuffer epitaxy layer is grown on, for example, a silicon substrate atthe beginning of the process flow. The process includes oxygen diffusionthrough the rare earth oxide buffer layer to the silicon substrateinterface, thereby forming a bottom silicon dioxide (SiO₂) dielectriclayer. Utilizing the lattice matching (which can be heteroepitaxy ordomain matching epitaxy) from the rare earth oxide buffer layer, ananosheet layer stack (e.g., silicon germanium/silicon nanosheet layers)is epitaxially grown for downstream nanosheet device processes.Accordingly, the bottom dielectric isolation layer isolates thesource/drain regions from the substrate and/or isolates the nanosheetregion from the substrate.

Turning now to a more detailed description of aspects of the presentinvention, FIG. 1A depicts a simple diagram of a top-down view of asemiconductor device 100 according to embodiments of the invention. FIG.1A is only for reference and illustrates a top-down view of locations ofthe nanosheets and gates for orientation purposes. For simplicity andease of understanding, FIG. 1A omits some layers (elements) so as to notobscure the figure.

FIG. 1B depicts a cross-sectional view of the semiconductor device 100shown in FIG. 1A taken along line X according to embodiments of theinvention. In FIG. 1B, the semiconductor device 100 is a nanosheet FETdevice. The semiconductor device 100 has a bottom dielectric isolationlayer 104 formed on a substrate 102. A rare earth material layer 106 hasbeen formed on top of the bottom dielectric isolation layer 104.

Nanochannel layers 108A, 108B, 108C are formed over the bottomdielectric isolation layer 104. The nanochannel layers 108A, 108B, 108Care formed of nanosheet layers. Source and drain (S/D) epitaxial regions110 are formed on ends of the nanochannel layer 108A, 108B, 108C.Inter-level dielectric (ILD) material 112 is formed on the S/D epitaxialregions 110. Spacers 114 are formed over the nanochannel layers 108A,108B, 108C. A dielectric material 116 is formed around the nanochannellayers 108A, 108B, 108C, and work function material(s) 118 are formedaround the dielectric material 116. A metal gate material 122 is formedon the work function material 118. A self-aligned contact (SAC) cap 120is formed on top of the dielectric material 116, work function material118, and metal gate material 122. Further details of fabricating thesemiconductor device 100 are discussed below.

FIG. 2 depicts a cross-sectional view of the semiconductor device 100shown in FIG. 1A taken along line X according to embodiments of theinvention. FIG. 3 depicts a cross-sectional view of the semiconductordevice 100 shown in FIG. 1A taken along line X according to embodimentsof the invention. In FIG. 2, the rare earth material layer 106 isdeposited on top of the substrate 102. The rare earth material layer 106can have a thickness in a range of, for example, about 5 nm-20 nm. Therare earth material layer 106 is epitaxially grown from the substrate102 so as to have lattice matching to the substrate 102 below. The rareearth material layer 106 is a buffer epitaxial layer on the substrate102. The substrate 102 is formed of semiconductor material. Thesubstrate 102 can be a silicon (Si) substrate, although other materialscan be used. The substrate 102 can be a wafer. The rare earth materiallayer 106 is a rare earth oxide material, which is used in an oxygendiffusion process 204 of oxygen molecules 202 (e.g., O₂) to create thebottom dielectric isolation layer 104 depicted in FIG. 3

In some embodiments of the invention, the rare earth material layer 106includes cubic rare earth oxides because the experimenters havedetermined that cubic rare earth oxides work better with, for example, asilicon substrate 102 in preparation to form a nanosheet stack.Particularly, cubic rare earth oxides like Gd₂O₃ with a lattice constant10.81 Å, Nd₂O₃ with a lattice constant 11.08 Å, and Er₂O₃ with a latticeconstant 10.55 Å are nearly twice that of silicon with a latticeconstant 5.43 Å. Cubic rare earth oxides (such, as for example, Gd₂O₃,Nd₂O₃, Er₂O₃, etc.) having a lattice constant about twice the latticeconstant of silicon are thus considered to be compatible with silicon,and consequently, crystalline rare earth oxides can be epitaxially grownon a silicon substrate, as depicted in FIG. 2. More examples of cubicrare earth oxides for rare earth material layer 106 include Y₂O₃, Pr₂O₃,Tb₂O₃, etc. Other rare earth oxide materials that can be utilized whichhave similar lattice constants include Sm₂O₃ with lattice constant 10.93Å and Dy₂O₃ with lattice constant 10.67 Å, and they yield latticemismatch values of 0.663% compressive, and 1.78% tensile, respectively,in either epitaxial orientation to silicon.

Additionally, in some embodiments of the invention, pseudocubic rareearth oxides can also be utilized as the rare earth material layer 106.An example pseudocubic rare earth oxide is LaAlO₃ with a latticeconstant of 3.82 Å and can be deposited at a 45° angle with respect tothe lattice of a silicon substrate. Epitaxial lattice matching could beachieved between the film and substrate in various ways, for example,using an inline 45° degree crystal rotation.

Referring back to FIG. 2, the oxygen diffusion process 204 occurs inchamber such as a vacuum chamber. During the oxygen diffusion process204, oxygen molecules 202 diffuse through the capping layer of the rareearth material layer 106 to the silicon substrate interface 206 and formthe bottom dielectric isolation layer 104 depicted in FIG. 3. Continuingthe example scenario in which the substrate 102 is silicon, as theoxygen molecules 202 diffuse through the rare earth material layer 106and reach the surface (interface 206) of the silicon substrate 102, theoxygen molecules 202 combine with the silicon to form silicon dioxide(SiO₂) resulting in the bottom dielectric isolation layer 104. In oneexample, the rare earth oxide/silicon wafer is exposed to O₂ (infusedinto the chamber) at high temp (e.g., about 500° C.-700° C.) before thenanostack growth, for oxygen diffusion into the substrate therebyforming the SiO₂ bottom dielectric isolation layer 106. The thickness ofthe bottom dielectric isolation layer 104 can range from about 5 nm-20nm. Although silicon is utilized to form silicon dioxide in thisexample, other substrate materials can be utilized to form an oxide.

Additionally, there can be options for higher oxidation rates. As oneoption for oxygen drive in, active oxygen species from electroncyclotron resonance (ECR) can be used, which results in a 4 to 5 foldincrease in the oxygen rate on silicon. Accordingly, the thickness ofthe bottom dielectric isolation layer 104 can range from about 5 nm-50nm. As another option for oxygen drive in, an atomic oxygen source canbe used, which results in a 5 to 10 fold increase in the oxidation rateon silicon. Additionally, a thicker bottom isolation dielectric layer(SiO₂) could be formed by a higher diffusivity of molecular oxygenthrough the interfacial silicate layer between the rare earth oxidelayer 106 and the silicon substrate 102.

FIG. 4 depicts a cross-sectional view of the semiconductor device 100shown in FIG. 1A taken along line X according to embodiments of theinvention. An epitaxial nanosheet stack 450 is formed. The epitaxialnanosheet stack 450 includes sacrificial layers 402 alternatingly formedwith channel layer 108A, 108B, and 108C.

The channel layer 108A, 108B, and 108C can be generally referred to aschannel layers 108. Although three channel layers 108 are shown, more orfewer channel layers 108 can be used, and the number of sacrificiallayers 402 will be increased or decreased accordingly. The sacrificiallayers 402 and channel layers 108 can be epitaxially grown. The latticematching of, for example, heteroepitaxy or domain matching epitaxy, fromthe rare earth oxide layer 106 (capping layer) is used to growepitaxially SiGe/Si nanosheet stack 450. The SiGe/Si nanosheet stack 450does not directly contact the substrate 102. Instead, the SiGe/Sinanosheet stack 450 is formed on the rare earth oxide layer 106.

The sacrificial layers 402 are formed of a material that can be removed(i.e., etched) without etching the layers 108 in the stack 450. Thesacrificial layers 402 can be silicon germanium (SiGe) which can beetched selective to silicon (e.g., silicon channel layers 108). Thethickness or height of each sacrificial layer 402 can range from about 5nm to 15 nm, and the height of each channel layer 108 can range fromabout 5 nm to 15 nm.

FIG. 5 depicts a cross-sectional view of the semiconductor device 100shown in FIG. 1A taken along line X according to embodiments of theinvention. A dummy gate layer 502 is formed on top of the uppersacrificial layer 402. The dummy gate layer 502 can be polycrystallinesilicon (poly silicon), amorphous silicon, and/or an oxide, such as,SiO₂. A gate hardmask 504 is formed on the dummy gate material. The gatehardmask 504 can be a nitride, oxide, and/or a combination nitride andoxide material.

FIG. 6 depicts a cross-sectional view of the semiconductor device 100shown in FIG. 1A taken along line X according to embodiments of theinvention. Dummy gate etch and spacer deposition are performed. Forexample, gate patterning is formed by patterning the gate hardmask 504and then using the patterned gate hardmask 504 to etch the dummy gatematerial 502 into the dummy gates 602. A spacer 114 is deposited on thetop surface, and chemical mechanical planarization/polishing (CMP) canbe performed to remove the spacer 114 from the top surface of thepatterned gate hardmask 504.

FIG. 7 depicts a cross-sectional view of the semiconductor device 100shown in FIG. 1A taken along line X according to embodiments of theinvention. Spacer etch and fin recess are performed. For example,reactive ion etch (RIE) can be performed to remove portions of thespacer 114 from the top of the nanosheet stack 450, such that portionsof the nanosheet stack 450 are exposed. A fin recess etch is performedto etch the sacrificial layers 402 and channel layers 108 of thenanosheet stack 450 stopping on the rare earth material layer 106,thereby creating openings 702 in preparation for source and drainregions. Directional RIE can be used during the fin recess.

FIG. 8 depicts a cross-sectional view of the semiconductor device 100shown in FIG. 1A taken along line X according to embodiments of theinvention. Formation of source or drain (S/D) epitaxial regions 110 isperformed. The S/D epitaxial regions 110 can be NFET source/drainepitaxial regions or PFET source/drain epitaxial regions according toformation of the NFET or PFET devices. Accordingly, the S/D epitaxialregions 110 can be doped with N-type dopants or P-type dopants asdesired. The S/D epitaxial regions 110 can be epitaxially grown from theedges of the channel layers 108.

FIG. 9 depicts a cross-sectional view of the semiconductor device 100shown in FIG. 1A taken along line X according to embodiments of theinvention. An inter-level dielectric (ILD) material 112 is deposited tocap the S/D epitaxial regions 110. The ILD material 112 is a low-kdielectric material such as, for example, an oxide material like silicondioxide. The ILD material 112 is then recessed by chemical mechanicalpolishing (CMP) until the gate hardmask layer 504 is reached.

A replacement metal gate (RMG) process is performed, as depicted inFIGS. 10, 11, and 12. FIG. 10 depicts a cross-sectional view of thesemiconductor device 100 shown in FIG. 1A taken along line X accordingto embodiments of the invention. The gate hardmask 504 is removed, andthe dummy gate etch (e.g., poly pulldown) of the dummy gate material 502is performed, resulting in trenches 1002 as depicted in FIG. 10. FIG. 11depicts a cross-sectional view of the semiconductor device 100 shown inFIG. 1A taken along line X according to embodiments of the invention.Nanosheet channel release is performed. For example, etching isperformed to remove the (SiGe) sacrificial layers 402 selective to thechannel layers 108 (i.e., without removing the channel layers 108). Inother words, the selective etching of the sacrificial layers 402releases the channel layers 108, thereby creating openings 1102 betweenthe channel layers 108. FIG. 12 depicts a cross-sectional view of thesemiconductor device 100 shown in FIG. 1A taken along line X accordingto embodiments of the invention. Conformal high-k metal gate (HKMG)formation is performed to deposit HKMG layers which fill the previousopenings 1002 and 1102. For example, dielectric layer 116 is depositedso as to wrap around the channel layers 108. One or more work functionmaterials 118 are formed on the dielectric layer 116. Optionally, ametal gate layer 122 can be formed on the work function material 118.The metal gate layer 122 can include tungsten (W), copper (Cu), etc.

The dielectric layer 116 is a high-k gate dielectric material, forexample, a dielectric material with a dielectric constant that isgreater than the dielectric constant of silicon dioxide (i.e., greaterthan 3.9). Exemplary high-k dielectric materials include, but are notlimited to, hafnium (Hf)-based dielectrics (e.g., hafnium oxide, hafniumsilicon oxide, hafnium silicon oxynitride, hafnium aluminum oxide, etc.)or other suitable high-k dielectrics (e.g., aluminum oxide, tantalumoxide, zirconium oxide, etc.).

The work function material can include a work function metal that isimmediately adjacent to the gate dielectric layer and that ispreselected in order to achieve an optimal gate conductor work functiongiven the conductivity type of the nanosheet-FET. For example, theoptimal gate conductor work function for the PFETs can be, for example,between about 4.9 eV and about 5.2 eV. Exemplary metals (and metalalloys) having a work function within or close to this range include,but are not limited to, ruthenium, palladium, platinum, cobalt, andnickel, as well as metal oxides (aluminum carbon oxide, aluminumtitanium carbon oxide, etc.) and metal nitrides (e.g., titanium nitride,titanium silicon nitride, tantalum silicon nitride, titanium aluminumnitride, tantalum aluminum nitride, etc.). The optimal gate conductorwork function for NFETs can be, for example, between 3.9 eV and about4.2 eV. Exemplary metals (and metal alloys) having a work functionwithin or close to this range include, but are not limited to, hafnium,zirconium, titanium, tantalum, aluminum, and alloys thereof, such as,hafnium carbide, zirconium carbide, titanium carbide, tantalum carbide,and aluminum carbide. The metal layer 122 can further include a fillmetal or fill metal alloy, such as tungsten, a tungsten alloy (e.g.,tungsten silicide or titanium tungsten), cobalt, aluminum or any othersuitable fill metal or fill metal alloy.

FIG. 13 depicts a cross-sectional view of the semiconductor device 100shown in FIG. 1A taken along line X according to embodiments of theinvention. A metal recess can be performed to recess the work functionmaterial 118 and the metal gate layer 122 in preparation to deposit theself-aligned contact (SAC) cap 120 depicted in FIG. 1B. The SAC cap 120is an insulating material, such as, a nitride (e.g., SiN), an oxide(e.g., SiO₂), etc.

According to embodiments of the invention, a method of forming asemiconductor device 100 is provided. The method includes forming a rareearth material 106 on a substrate 102, forming an isolation layer 104 atan interface 206 of the rare earth material 106 and the substrate 102,forming channel layers 108 over the isolation layer 104, and formingsource or drain (S/D) regions 110 on the isolation layer 104.

Also, the method includes forming a dielectric layer 116 on the channellayers 108A, 108B, 108C, and forming one or more work function materials118 on the channel layers 108. The one or more work function materials118 are on the isolation layer 104. The isolation layer 104 separates aportion of the one or more work function materials 118 from thesubstrate 102. The isolation layer 104 physically separates andelectrically isolates the S/D regions 110 from the substrate 102.

The rare earth material 106 is a rare earth oxide. The rare earthmaterial 106 is a rare earth oxide with a cubic lattice. The rare earthmaterial 106 is a rare earth oxide having a lattice constant that isabout twice a lattice constant of a material of the substrate 102. Alattice structure of the rare earth material 106 about matches a latticestructure of the channel layers 108.

Also, the method includes forming the isolation layer 104 at theinterface 206 of the rare earth material 106 on the substrate 102includes diffusing oxygen through the isolation layer 104 and growingthe isolation layer 104 at the interface 206. The isolation layer 104 isan oxide material. The isolation layer 104 is formed as an oxide of amaterial of the substrate 102.

According to embodiments of the invention, a method of forming anisolation layer 104 for a semiconductor device 100. The method includesforming a rare earth oxide material 106 on a substrate 102, diffusingoxygen 204 through the rare earth material 106 such that an oxide isgrown at an interface 206 of the rare earth oxide material and thesubstrate, the oxide being the isolation layer 104. The method includesforming channel layers 108 over the isolation layer 104 and formingsource or drain (S/D) regions 110 on the isolation layer 104.

Terms such as “epitaxial growth” and “epitaxially formed and/or grown”refer to the growth of a semiconductor material on a deposition surfaceof a semiconductor material, in which the semiconductor material beinggrown has the same crystalline characteristics as the semiconductormaterial of the deposition surface. In an epitaxial deposition process,the chemical reactants provided by the source gases are controlled andthe system parameters are set so that the depositing atoms arrive at thedeposition surface of the semiconductor substrate with sufficient energyto move around on the surface and orient themselves to the crystalarrangement of the atoms of the deposition surface. Therefore, anepitaxial semiconductor material has the same crystallinecharacteristics as the deposition surface on which it is formed. Forexample, an epitaxial semiconductor material deposited on a {100}crystal surface will take on a {100} orientation.

Various embodiments of the present invention are described herein withreference to the related drawings. Alternative embodiments can bedevised without departing from the scope of this invention. Althoughvarious connections and positional relationships (e.g., over, below,adjacent, etc.) are set forth between elements in the followingdescription and in the drawings, persons skilled in the art willrecognize that many of the positional relationships described herein areorientation-independent when the described functionality is maintainedeven though the orientation is changed. These connections and/orpositional relationships, unless specified otherwise, can be direct orindirect, and the present invention is not intended to be limiting inthis respect. Accordingly, a coupling of entities can refer to either adirect or an indirect coupling, and a positional relationship betweenentities can be a direct or indirect positional relationship. As anexample of an indirect positional relationship, references in thepresent description to forming layer “A” over layer “B” includesituations in which one or more intermediate layers (e.g., layer “C”) isbetween layer “A” and layer “B” as long as the relevant characteristicsand functionalities of layer “A” and layer “B” are not substantiallychanged by the intermediate layer(s).

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” are understood to include any integer number greaterthan or equal to one, i.e. one, two, three, four, etc. The terms “aplurality” are understood to include any integer number greater than orequal to two, i.e. two, three, four, five, etc. The term “connection”can include an indirect “connection” and a direct “connection.”

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment may or may not include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper,” “lower,”“right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” andderivatives thereof shall relate to the described structures andmethods, as oriented in the drawing figures. The terms “overlying,”“atop,” “on top,” “positioned on” or “positioned atop” mean that a firstelement, such as a first structure, is present on a second element, suchas a second structure, wherein intervening elements such as an interfacestructure can be present between the first element and the secondelement. The term “direct contact” means that a first element, such as afirst structure, and a second element, such as a second structure, areconnected without any intermediary conducting, insulating orsemiconductor layers at the interface of the two elements.

The phrase “selective to,” such as, for example, “a first elementselective to a second element,” means that the first element can beetched and the second element can act as an etch stop.

The terms “about,” “substantially,” “approximately,” and variationsthereof, are intended to include the degree of error associated withmeasurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

As previously noted herein, for the sake of brevity, conventionaltechniques related to semiconductor device and integrated circuit (IC)fabrication may or may not be described in detail herein. By way ofbackground, however, a more general description of the semiconductordevice fabrication processes that can be utilized in implementing one ormore embodiments of the present invention will now be provided. Althoughspecific fabrication operations used in implementing one or moreembodiments of the present invention can be individually known, thedescribed combination of operations and/or resulting structures of thepresent invention are unique. Thus, the unique combination of theoperations described in connection with the fabrication of asemiconductor device according to the present invention utilize avariety of individually known physical and chemical processes performedon a semiconductor (e.g., silicon) substrate, some of which aredescribed in the immediately following paragraphs.

In general, the various processes used to form a micro-chip that will bepackaged into an IC fall into four general categories, namely, filmdeposition, removal/etching, semiconductor doping andpatterning/lithography. Deposition is any process that grows, coats, orotherwise transfers a material onto the wafer. Available technologiesinclude physical vapor deposition (PVD), chemical vapor deposition(CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE)and more recently, atomic layer deposition (ALD) among others.Removal/etching is any process that removes material from the wafer.Examples include etch processes (either wet or dry), andchemical-mechanical planarization (CMP), and the like. Semiconductordoping is the modification of electrical properties by doping, forexample, transistor sources and drains, generally by diffusion and/or byion implantation. These doping processes are followed by furnaceannealing or by rapid thermal annealing (RTA). Annealing serves toactivate the implanted dopants. Films of both conductors (e.g.,poly-silicon, aluminum, copper, etc.) and insulators (e.g., variousforms of silicon dioxide, silicon nitride, etc.) are used to connect andisolate transistors and their components. Selective doping of variousregions of the semiconductor substrate allows the conductivity of thesubstrate to be changed with the application of voltage. By creatingstructures of these various components, millions of transistors can bebuilt and wired together to form the complex circuitry of a modernmicroelectronic device. Semiconductor lithography is the formation ofthree-dimensional relief images or patterns on the semiconductorsubstrate for subsequent transfer of the pattern to the substrate. Insemiconductor lithography, the patterns are formed by a light sensitivepolymer called a photo-resist. To build the complex structures that makeup a transistor and the many wires that connect the millions oftransistors of a circuit, lithography and etch pattern transfer stepsare repeated multiple times. Each pattern being printed on the wafer isaligned to the previously formed patterns and slowly the conductors,insulators and selectively doped regions are built up to form the finaldevice.

The flowchart and block diagrams in the Figures illustrate possibleimplementations of fabrication and/or operation methods according tovarious embodiments of the present invention. Variousfunctions/operations of the method are represented in the flow diagramby blocks. In some alternative implementations, the functions noted inthe blocks can occur out of the order noted in the Figures. For example,two blocks shown in succession can, in fact, be executed substantiallyconcurrently, or the blocks can sometimes be executed in the reverseorder, depending upon the functionality involved.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments described. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdescribed herein.

What is claimed is:
 1. A method of forming a semiconductor device, themethod comprising: forming a rare earth material in direct contact withand on a substrate; forming an isolation layer at an interface betweenand in direct contact with both the rare earth material and thesubstrate; forming channel layers over the isolation layer; and formingsource or drain (S/D) regions on the isolation layer, the S/D regionsand the isolation layer sandwiching the rare earth material, the S/Dregions being in direct contact with the rare earth material.
 2. Themethod of claim 1 further comprising forming a dielectric layer on thechannel layers.
 3. The method of claim 2 further comprising forming oneor more work function materials on the channel layers.
 4. The method ofclaim 2, wherein the one or more work function materials are on theisolation layer.
 5. The method of claim 2, wherein the isolation layerseparates a portion of the one or more work function materials from thesubstrate.
 6. The method of claim 1, wherein the isolation layerphysically separates and electrically isolates the S/D regions from thesubstrate.
 7. The method of claim 1, wherein the rare earth materialcomprises a rare earth oxide.
 8. The method of claim 1, wherein the rareearth material comprises a rare earth oxide with a cubic lattice.
 9. Themethod of claim 1, wherein the rare earth material comprises a rareearth oxide having a lattice constant that comprises about twice alattice constant of a material of the substrate.
 10. The method of claim1, wherein a lattice structure of the rare earth material substantiallymatches a lattice structure of the channel layers.
 11. The method ofclaim 1, wherein forming the isolation layer at the interface of therare earth material on the substrate comprises diffusing oxygen throughthe isolation layer and growing the isolation layer at the interface.12. The method of claim 1, wherein the isolation layer comprises anoxide material.
 13. The method of claim 1, wherein the isolation layeris formed as an oxide of a material of the substrate.
 14. A method offorming an isolation layer for a semiconductor device, the methodcomprising: forming a rare earth oxide material in direct contact withand on a substrate; diffusing oxygen through the rare earth oxidematerial such that an oxide is grown at an interface between and indirect contact with both the rare earth oxide material and thesubstrate, the oxide being the isolation layer; forming channel layersover the isolation layer; and forming source or drain (S/D) regions onthe isolation layer, the S/D regions and the isolation layer sandwichingthe rare earth material, the S/D regions being in direct contact withthe rare earth material.